U.S. patent application number 11/127787 was filed with the patent office on 2006-11-16 for dynamic display optimization method and system with image motion.
This patent application is currently assigned to L-3 Communications Corporation. Invention is credited to James A. Turner.
Application Number | 20060256140 11/127787 |
Document ID | / |
Family ID | 36646074 |
Filed Date | 2006-11-16 |
United States Patent
Application |
20060256140 |
Kind Code |
A1 |
Turner; James A. |
November 16, 2006 |
Dynamic display optimization method and system with image
motion
Abstract
A system displays video to a user and has a display device with
a field of pixels. It displays video to the user in the form of a
series of discrete sequential frame images each made up of a first
predetermined number of bit planes in which the pixels of the
display are either off or have a color and intensity that is
uniform over the field of pixels. The apparatus detects when a
movement condition is present, such as rapid head movement or an
object in the video crossing the display rapidly, in which
condition the user's eye may tend to track across the display
device at a rate at which perception of the video displayed may be
reduced in quality, and it generates a condition-present signal
when such a movement condition is detected. Responsive to
generation of said condition-present signal, the apparatus causes
the display device to display the frame images using fewer bit
planes for each frame image than when said movement condition is
not detected. Display with the original number of bit planes
returns when the movement condition is over.
Inventors: |
Turner; James A.;
(Binghamton, NY) |
Correspondence
Address: |
TIAJOLOFF & KELLY
CHRYSLER BUILDING, 37TH FLOOR
405 LEXINGTON AVENUE
NEW YORK
NY
10174
US
|
Assignee: |
L-3 Communications
Corporation
New York
NY
|
Family ID: |
36646074 |
Appl. No.: |
11/127787 |
Filed: |
May 11, 2005 |
Current U.S.
Class: |
345/690 |
Current CPC
Class: |
G09B 9/307 20130101 |
Class at
Publication: |
345/690 |
International
Class: |
G09G 5/10 20060101
G09G005/10 |
Claims
1. A method of displaying to a user video made up of a sequence of
frames, said method comprising: displaying a first portion of said
video to a user by displaying using a display device a first series
of frame images each corresponding to a respective one of said
frames and each being made up of a first predetermined number of
sequentially displayed bit-plane images that are all displayed in a
first frame display period defined by a duration of time from the
beginning of the display of the first of said bit planes of the
frame image to the end of the display of the last of the bit planes
of the frame image; detecting automatically in real time whether a
movement condition is present that may give rise to a degradation
of the perceived quality of the video display; displaying using
said display device, responsive to a detection of said movement
condition, a second portion of said video by displaying a second
series of frame images each corresponding to a respective one of
said frames and each being made up of sequentially displayed
bit-plane images that are all displayed in a second frame display
period defined by a duration of time from the beginning of the
display of the first of said bit planes of the frame image to the
end of the display of the last of the bit planes of the frame
image; said second frame display period being shorter than said
first frame display period.
2. The method of claim 1, wherein each frame image of said second
portion of said video is made up of a second predetermined number
of bit plane images that is fewer than said predetermined number of
bit plane images of the first portion of said video.
3. The method of claim 1 wherein the presence of said movement
condition is detected based on a measure of a rate of rotation of
the head of the user by comparing said measure of the rate of
rotation of the head of the user to a preselected threshold rate
value and then determining presence of the movement condition when
the measure of the rate of rotation is greater than or equal to
said threshold rate value.
4. The method of claim 3 wherein said measure of the rate of
rotation of the head of the user is derived from a signal from a
head tracking device detecting movement of the head of the
user.
5. The method of claim 1 wherein the presence of said movement
condition is detected based on an analysis of said video to
determine when said video has a characteristic that tends to cause
tracking of the eye of the user across the frame images
thereof.
6. The method of claim 1 wherein the video is transmitted to a
display controller that transmits electrical signals that control
the display device that displays the frame images to the user.
7. The method of claim 6 wherein said display controller modifies
the video for display dependent on an indication of whether the
movement condition is present such that the number of bit planes
making up the frame images displayed and the frame display period
are reduced when the movement condition is detected.
8. The method of claim 7 wherein, when said movement condition is
detected, a signal indicative of the presence thereof is sent to
the display controller.
9. The method of claim 8 wherein the video is transmitted to the
display controller as a digital video signal in which each pixel of
each frame has a color defined by a predetermined resolution number
of bits, and wherein the second predetermined number of bit planes
in the second portion of video displayed by the display controller
responsive to said signal indicative of the presence of the
movement condition is less than the predetermined resolution number
of bits.
10. The method of claim 1 wherein said method further comprises
generating said video using a computerized image generating
system.
11. The method of claim 1 wherein said frame images are displayed
on an LCD display device.
12. The method of claim 1 wherein said frame images are displayed
on a head mounted display device.
13. The method of claim 2 wherein the detecting of the movement
condition includes detecting at least two levels of said movement
condition where each level represents a different degree of
potential degradation of perception of the video by the user, and,
responsive to detection of a first lower level of said movement
condition, said video is displayed in frame images having more no
more than said second predetermined number of bit planes, and
responsive to a detection of a second higher level of movement
condition, said video is displayed in frame images having no more
than a third predetermined number of bit planes that is less than
said second predetermined number of bit planes.
14. The method of claim 2 wherein the first predetermined number of
bit planes is 24 bit planes, and the second predetermined number of
bit planes is 21 or fewer bit planes.
15. The method of claim 1 wherein the second portion of video is
derived by converting video digital data defining the frames to
scaled data with a lower resolution.
16. The method of claim 1 wherein the second portion of the video
is derived by dropping the least significant bit data from video
digital data defining the frames of the video.
17. The method of claim 2 wherein the display is a color display
and the video is 24-bit color video, and each of the bit planes is
a field of on or off pixels that is all red, all blue or all
green.
18. The method of claim 2 wherein, when said movement condition is
no longer detected, a third portion of said video is displayed by
displaying a third series of frame images each corresponding to a
respective one of said frames of said video and each being made up
of the first predetermined number of sequentially displayed
bit-plane images.
19. A system for displaying video to a user, said system
comprising: a display device having a field of pixels and
displaying video to the user in the form of a series of discrete
sequential frame images each being made up of a respective series
of a first predetermined number of bit planes in which the pixels
of the display are either off or have a color and intensity that is
uniform over the field of pixels; an apparatus detecting when a
movement condition is present that may cause a degradation of
perception of the video displayed, and, responsive to generation of
said condition-present signal, causing the display device to
display the frame images using fewer bit planes for each frame
image than when said movement condition is not detected.
20. The system of claim 19, and further comprising a head tracking
apparatus detecting a position, orientation or movement of the
user's head and generating data indicative thereof, said movement
condition being detected when the data from said head tracking
apparatus indicates a rate of rotation of the head of the user that
is greater than or equal to a predetermined threshold value.
21. The system of claim 19 wherein the apparatus includes an image
generator generating said video frame images, and wherein the
apparatus detects presence of said movement condition when the
video output has a characteristic that tends to make the eye of the
user track a virtual object across the display device.
22. The system of claim 19 wherein the video is supplied as digital
color video defining sequential frames of pixels where each pixel
has a color definition data value defined by three sets of bits,
each set of bits corresponding to a respective display color of the
group consisting of red, blue and green; said apparatus displaying
said series of bit planes as each red, green or blue, and said
apparatus reformulating the color definition data value of each
pixel with at least one bit fewer in each of said sets of bits and
causing the display device to display the frame images using a
reduced number of bit planes corresponding to said reformulated
color definition.
23. The system of claim 22 wherein said reformulating of the color
definition includes converting said color definition data value to
a reformulated data value scaled proportionately to a possible
range of values that can be stored in the reduced number of bits
allotted to the reformulated data value.
24. The system of claim 19 wherein said condition present signal
contains a level value derived by a calculation of a degree of
severity of said motion condition, and said apparatus displaying
said frame images with a first number of bit planes per frame image
when said level value has a first value, and displaying said frame
images with a second number of bit planes per frame image that is
less than the first number when said level value has a second value
different from said first value.
25. The system of claim 19 wherein said apparatus detects when the
movement condition ceases to be present, and, responsive to said
detection that the movement condition is no longer present,
displaying the frame images on the display device with said first
predetermined number of bit planes for each of said frame
images.
26. The system of claim 19 wherein said display device is a
helmet-mounted display system.
27. A system comprising: a display device supported on the head of
a user and displaying images to the user on a visor using bit
planes of three primary colors; a head tracking apparatus providing
a head tracking signal containing data from which the position,
movement or orientation of a user's head can be derived; an image
generator receiving said head tracking signal and, based at least
in part thereon, generating real-time digital video comprising
sequential digital frame images of pixels wherein each pixel has a
color defined by at least eight bits per primary display color;
said image generator continually detecting based at least in part
or said head tracking signal whether the head of the user is
rotating at a rate of rotation that has reached or exceeded a
threshold rate value, and generating a condition-present signal
when said rate of rotation has reached or exceeded said threshold
rate value; the display device having a circuit receiving the video
and the condition-present signal from the image generator; said
display device displaying the current frame image of the video on
said visor in a first color-depth when the condition present signal
is not received, and displaying the current frame image in a lower
color depth and with fewer than said first number of bit planes
when the condition present signal is received.
28. The system of claim 27 wherein the image generator has a mapper
modifying the video for the display device generator and the light
engine.
Description
FIELD OF THE INVENTION
[0001] This invention relates to systems and methods for displaying
video to a user, and especially to systems that involve displaying
video images using sequentially-displayed bit planes.
BACKGROUND OF THE INVENTION
[0002] As is well known in the art, video is displayed to a viewer
by displaying a series of still frame images sequentially on a
display. The images are displayed one after another at a rate that
is fast enough so that it appears to the normal human eye that the
movement of objects in the video is smooth and continuous. In
digital video, each frame image is made up of pixels that each have
a respective color intensity for each of the primary display colors
(red, green, and blue). The digital value of each primary color
intensity of the pixel is frequently defined by eight bits of data,
allowing for definition of up to 255 levels of intensity for each
color, and an eight-bit color depth of a possible
255.times.255.times.255=16,581,375 colors, ranging from black
(0,0,0) to white (255, 255, 255).
[0003] In some digital video displays, especially LCD or liquid
crystal on silicon (LCOS) displays, each still frame image of the
video is in fact a series of one-color component frames, called bit
planes, that are displayed in a series and add up to the total
color frame image. In each bit plane, the pixels are either on or
off, and those pixels that are on in the bit plane are all on in
the same primary color and intensity.
[0004] Each bit plane corresponds to a respective bit in the set of
digital data defining the color of the pixels. For example, in some
systems, the first bit plane displayed corresponds to the
most-significant bit of the red image for all of the pixels at the
maximum red intensity for the display, then the next bit plane at
half that red intensity for the next most significant red bit,
etc., down to the last red bit plane corresponding to the least
significant red bit, wherein all the pixels have a red intensity of
1/128 of the maximum red intensity. After the red planes, the green
bit planes corresponding to the most significant to the least
significant green pixel bits are similarly displayed, and then the
blue bit planes.
[0005] The twenty-four bit planes are displayed so quickly that the
total frame image display duration, i.e., the time from the start
of the display of the first bit plane of the frame image to the end
of the display of the last bit plane of that same frame, is less
than the cycle time for display of each sequential image of the
video, and the user normally sees only a moving video image, not
individual bit planes or individual frame images.
[0006] In some environments, however, such as simulators for
aircraft, bit-plane displays can be subject to some undesirable
perception effects where the video being displayed has certain
characteristics, or when the user's eyes pan or track across the
image, so as to result in relatively rapid movement of the eye of
the viewer relative to the objects seen in the displayed
imagery.
[0007] In a simulator, usually there is a display that shows the
user a real-time simulated out-the-window ("OTW") view from the
aircraft, and possibly other objects like simulated head-up display
imagery, all of which are created by an image generating computer
system to give realism to the simulation. The display frequently is
a head-mounted display in which the user wears a helmet fitted with
a visor and a head tracking apparatus. An image generator transmits
digital video appropriate to the simulation and to the direction
that the head tracker indicates the user is looking. If the user
turns his head rapidly, the head tracker detects this, and the
image generator makes the scene displayed on the visor move rapidly
to one side or another to conform to the new point of view.
[0008] As the user turns his head, however, his eyes move more or
less continuously across the field of view, i.e., across the field
of objects visible in the display device. The video, in contrast to
the continuous movement of the eye, is a series is a series of
still color images, each of which is made up of a series of frames,
each of which is made up of a subset of still bit-plane images in
which virtual objects in the simulated video display, like a
passing aircraft, or the entire field of view when the simulated
ownship is rotating or moving, is displayed as essentially in one
stationary location from the start of display of the first bit
plane to the end of display of the last bit plane of the given
frame image.
[0009] As illustrated in by FIG. 1, the effect of this on the
user's eye moving continuously relative to the object is that the
image of an object in early bit planes strikes the retina of the
user's eye in a different location compared to its location in
later bit planes of the same frame image, resulting in a perceived
separation into the colors of the different bit planes, which
degrades the realism of the simulation.
[0010] Rapid movement of various types may produce the problem of
tracking of the eyes across the display to give rise to a perceived
separation of the first and last bit planes. The usual source of
the problem is rapid head rotation. In addition, though, ownship
rotations in a simulation may give rise to tracking of the eye
relative to the displayed image that creates the separation of bit
planes, as may high-speed movement of an object relative to the
ownship.
SUMMARY OF THE INVENTION
[0011] It is therefore an object of the present invention to
provide a method that reduces or avoids the problem of perceived
separation of the bit planes, and allows for an improvement of the
display of video displayed using bit planes. This object is
accomplished by a method that comprises detecting when
artifact-causing movement conditions are present in which problems
with bit-plane displays occur, such as increased image movement or
rapid head movement of the user, and then taking action to modify
the displayed video so that the degradation of perception of the
video is reduced. In the preferred embodiment, the displayed video
is modified in response to the detection so that the frame image
display duration for images subject to these movement conditions is
shortened by reducing the length of time between the first and last
bit planes of each frame image, and consequently reducing the
perception of displaced separation of the bit plane images.
[0012] One method according to the invention comprises displaying a
first portion of video to a user by displaying, using a display
device, a first series of frame images each corresponding to a
respective frame of the video, and each made up of a first
predetermined number of sequentially displayed bit-plane images.
These bit-plane images are all displayed in a first frame display
period, defined as the duration of time from the beginning of the
display of the first of the bit plane images of the frame image to
the end of the display of the last of the bit planes of the frame
image. The method further comprises detecting automatically in real
time whether a movement condition is present that may give rise to
a movement of the eye of the user relative to the frame images at a
rate sufficient to create a degradation of the perceived quality of
the video display. Responsive to a detection of the movement
condition, a second portion of the video is displayed by displaying
a second series of frame images that each correspond to a
respective frame of the video and each are made up of a
predetermined number of sequentially displayed bit-plane images
that are all displayed in a second frame display period, defined as
the duration of time from the beginning of the display of the first
of the bit planes of the frame image to the end of the display of
the last of the bit planes of the frame image. The second frame
display period is shorter than the first frame display period.
[0013] According to a preferred embodiment of the invention, the
display time of the images is reduced by reducing the number of bit
planes displayed for each color of the frame image. If the color
video is displayed as 8 red bit planes, 8 green bit planes, and 8
blue bit planes, the display time for the frame may be reduced by
converting the video data to a lower color resolution (or lower
color depth) where the frame is made up of 7 red bit planes, 7
green bit planes, and 7 blue bit planes. This results in a frame
display duration that is 12.5% less than the normal video. It also
results in a loss of color precision, or color depth, since the
number of possible colors drops to
(2.sup.7).times.(2.sup.7).times.(2.sup.7)=2,097,152 possible colors
from the us (2.sup.8).times.(2.sup.8).times.(2.sup.8)=16,777,216
possible colors in the normal 24-bit color video.
[0014] In an alternate embodiment, the least significant bit plane
for each color can simply be dropped, and the more significant
seven bit planes for each color displayed.
[0015] If further shortening of the frame display duration is
desired, the video may be converted and displayed using even fewer
bit planes per frame, e.g., 6 bit planes per color, or 5 bit planes
per color, or fewer. As the number of bit planes is reduced,
however, the color resolution is reduced. Different degrees of
shortening of the frame display time may be applied dependent on
different detected levels of image movement that would tend to
degrade perception of the display.
[0016] The detection of artifact-causing movement conditions is
accomplished in the preferred embodiment by deriving a measure of
image movement from the input of a head tracking apparatus, if one
is present. It may also be determined by the image generator based
on changes of parameters in the scene data, data defining the point
of view of the user in the virtual world, or by a comparison of
sequential images of the video, or portions thereof. The measure or
indications of image movement are compared to pre-selected
parameters for triggering the reduced display time images, and a
signal indicating the presence, and preferably the severity, of the
movement condition is produced.
[0017] It is further an object of the invention to provide for a
return to normal video once the movement conditions indicative of
possible video artifacts are no longer detected, video is again
displayed using the usual number of bit planes per frame.
[0018] It is further an object of the present invention to provide
apparatus for practicing the above-described method.
[0019] According to another aspect of the invention, a system is
provided that comprises a display device displaying video to the
user in the form of a series of discrete sequential frame images
each being made up of a respective series of a first predetermined
number of bit planes in which the pixels of the display are either
off or have a color and intensity that is uniform over the field of
pixels of the display device. An apparatus detects when a movement
condition is present that may cause degradation of the quality of
perception of the video by the user, and, responsive to detection
of the movement condition, causes the display device to display the
frame images using fewer bit planes for each frame image than when
said movement condition is not detected.
[0020] Other objects and advantages of the invention will become
apparent in the specification herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagram of the distribution of the light from an
image in a bit plane display on the retina of a user as the eye
tracks across the field of view.
[0022] FIG. 2 is a diagram of a simulator system in which the
invention may be applied.
[0023] FIG. 3 is a schematic diagram of a simulator system
employing the inventive method.
[0024] FIG. 4 is a timeline diagram showing operation of the system
and method of the invention.
[0025] FIG. 5 is a detailed diagram illustrating a shortening of
the frame display times for varying levels of detected motion.
[0026] FIG. 6 is a diagram of the bit plane display produced in a
display device having a bit-plane sequencing controller.
DETAILED DESCRIPTION
[0027] As best seen in FIG. 2, in a simulator system for an
aircraft, the user is seated in a simulated cockpit structure 3
that includes dummy controls and gauges similar to those in the
real aircraft. A simulator computer system 2 controls the operation
of the simulator system to make the simulation as realistic as
possible. The simulator system also includes a display system that
gives the user a simulated real-time out-the-window (OTW) view that
is created by the simulator computer system 2, which includes an
image generation system in the form of hardware and software that
renders imagery video fast enough to keep up with the real-time
operation of the simulation. The display may be a projection
system, such as the system shown in U.S. Pat. No. 6,552,699, or any
of a variety of other projection or display systems. In the
preferred embodiment, the display system is a head-mounted display
system 5 supported on a helmet 7 on the head of the user. The
head-mounted display system 5 has a display device that includes
visor screen 9 in front of the user's eyes and a housing 11 that
supports therein image display electronics that transmit, project,
or otherwise form, a moving real-time image on visor screen 9 so as
to be seen by the user.
[0028] A head tracking apparatus 13 is supported on helmet 7. The
head tracking apparatus 13 may be any of the various tracking
systems well known in the art, such as an intersense accelerometer
associated with the helmet of the user, or a motion sensor
detecting the position and orientation of the user's head. Most
preferably, the head tracker is an ultrasonic system, in which one
or more ultrasonic signals are produced by a device on the user's
helmet and detected by microphones in the simulator to detect the
location and orientation of the user's head. Whatever the type of
head tracker used, the head tracker system generates electrical
signals related to the location, orientation and/or movement of the
head of the user, and from these signals the simulator computer
system determines the point of view to be used to render real-time
imagery for display on the head-mounted display visor 9.
[0029] As best shown in FIG. 3, the cockpit 3 has an output circuit
19 (generally, a circuit board with connectors to one or more
cables) that transmits various outputs from the cockpit 3,
including the output of the head tracking apparatus, to a host
computer 21 over communication line 20. Host computer system 21
receives the output from the simulated cockpit 3 and maintains data
for running the simulation in the cockpit 3, and optionally one or
more other cockpit simulator structures (not shown), which enable
multiple trainees to practice simulated group sorties or other
combined operations in a shared virtual world supported by the host
computer 21.
[0030] The host system 21 also includes or communicates with an
image generator 23, which may be understood to be software running
on the same computer system 21 or separate hardware and software
running in parallel, as is well known in the art. Typically, the
host computer computes data relating to the attributes of the
ownship simulated by cockpit structure 3, such as position,
orientation, roll, pitch, etc., and communicates this data to the
image generator. The host computer also transmits data derived from
the output of the head tracking device to the image generator 23 so
that the image generator is able to determine therefrom the point
of view for which it is rendering the OTW scene.
[0031] The image generator 23 contains or has access to an
electronically stored computer accessible database containing data
defining the scene and other virtual attributes of the simulated
vehicle environment and situation. From this scene data, which is
maintained in real time to reflect constant changes in the virtual
world being simulated, and from the user's time-varying viewpoint
and viewing direction in the virtual world, the image generator 23
renders the serial frame images for the OTW scene and any other
imagery shown to the user (e.g., head-up display symbology), and
transmits these frames as continuous digital color video. This
digital video signal is a series of frame images configured to be
displayed at an update cycle of 60 Hz, so as to appear to the user
to be a normally moving OTW scene. Each of the frame images is
preferably a set of digital data made up of three eight-bit data
fields per pixel, with each data field representing the intensity
of a respective primary color of the display, i.e., red, green or
blue, for the associated pixel. In the preferred embodiment, the
digital video is configured based on a field of 1280.times.1024
pixels.
[0032] The frames produced by the image generator are conceptually
rectangular. The display device, however, whether a projector or a
head mounted display, is often not a rectilinear display.
Accordingly, the video signal in the preferred embodiment is sent
from the image generator 23 to mapper circuitry 25, which
configures the video to prevent distortion thereof on the display
device. Particularly preferred for this purpose is a mapper sold
under the name "Mercator" by SEOS Ltd., a company with having an
office in West Sussex, U.K. This mapper 25 is an image distortion
correction system that allows fixed matrix projectors to be used in
curved screen applications, or also in other displays with
geometries that are in some way distortional. It receives the video
stream at full 24-bit color depth, `warps` the image and delivers a
modified 24-bit color depth video via communication line 27 to a
bit-plane-sequencing display controller or light engine 29 in the
cockpit structure 3. The light engine 29 receives the video and
controls display device 33 so as to appropriately display the video
received along line 27, as will be described below.
[0033] In the preferred embodiment, the image generator 23 also
detects whether there is a motion condition that may produce, or is
likely to produce, a degradation of perception of the video
displayed. When such a movement condition is detected, the image
generator transmits a condition-presence signal to light engine 29
along communications line 31, which is shown as independent of
video transmission line 27, but alternatively may be combined with
the transmission along the video line 27 if preferred. According to
the preferred embodiment, the signal is composed of three bits that
represent a number from zero to seven, and is used to indicate the
severity of the movement condition detected, with zero indicating
no movement condition being present.
[0034] The detection of the movement condition presence is
performed by image generator 23, although it may also be performed
by other components of the system, depending on how the condition
is detected.
[0035] In the most preferred embodiment, the movement condition is
detected based on a determination derived from the output of head
tracking system 13 of the rate of rotation of the user's head. In a
head mounted display, the rotation of the head of the user causes
the imagery on the visor 9 to shift across the display to provide
the proper view, and when the rotation is fast and larger in
displacement, such as when the user turns quickly from looking to
the left to suddenly looking to the right, the imagery displayed
also moves rapidly. In a bit-plane display, however, the movement
of the frames of the imagery is not continuous, but rather
sequential still frame images each composed of a subset of still
bit plane images in each of which the virtual objects in the video
are effectively stationary during the entire frame display period,
during which time the user's point of view is tracking continuously
across the virtual scene. The result is a potential of perceived
degradation of the video during the period of movement, as has been
discussed above. Head rotation preferably should be understood to
mean rotation about any axis, whether the movement of the head is
up and down or lateral, or a combination of the two.
[0036] The calculated or detected rotation of the user's head is
compared with one or more predetermined threshold values to detect
the motion condition. If the head rotation rate exceeds the
threshold rate value, a motion condition is detected and a signal
indicative of its presence is output to the light engine 29. In a
system where two or more incrementally increasing threshold values
are used, when the lowest threshold is exceeded, a signal
corresponding to 1 is output. If the next higher threshold value is
exceeded, then the condition presence signal output is set to 2,
and so on, for as many levels of movement-condition severity are
desired.
[0037] In the preferred embodiment, a threshold level of head
rotation that triggers a detection of the movement condition is 20
degrees/second. A higher level of rotation is detected as the rate
of head rotation passes 40 degrees/second, and the highest level
detection is in the area of 60 degrees/second. The output signal is
set to values of 1, 2 and 3, corresponding to reaching the
threshold values of 20, 40 and 60 degrees/second. These threshold
limits, however, may be adjusted, since different display devices
may have different degrees of sensitivity or physical parameters
that may require greater or lesser sensitivity for detecting the
condition.
[0038] In addition to head rotation, there are other aspects of the
video imagery itself that may tend to cause degraded perception of
the video. For example, even when the user's head is stationary,
the OTW scenery displayed might move rapidly one way or another due
to rapid ownship movement, for example by a sudden dive or bank of
the user's ownship in simulation. In an alternate embodiment, the
image generator 23 detects such a rapid imagery shift based on a
calculated value of rotation or other movement of the ownship from
the host system, or a calculated change in viewpoint from which the
video imagery is being rendered, or based on an analysis of the
video itself to detect its rapidly shifting point of view, such as
by comparison of sequential frame images. As with detection of the
movement condition based on head rotation data, the data value
being tested, e.g., virtual ownship rotation or a numerical
expression of the shifting of the video imagery, is compared with
one or more predetermined threshold values each representing a
respective level or degree of movement condition, and a signal is
output to the light engine 29 indicating the presence of the
condition, and preferably the severity level of the condition,
where more than one threshold is used.
[0039] In addition to changes in viewpoint due to real or virtual
changes in viewpoint, the video may have characteristics that are
artifact-causing, such as simply containing objects moving in it
across the display that may cause the user's eye to track them and
cause the perception of separation. Such an object might be, for
example, a simulated virtual aircraft flying near the user's
ownship that suddenly moves with respect thereto at a high enough
speed that the user's eye tracks it continuously, and sees color
separation due to the object being displayed as effectively
stationary in the several bit-planes of each frame over the frame
display period during its rapid movement. The image generator may
also be configured to analyze the scene data or the video frame
output to detect if there are one or more rapidly moving virtual
objects in the field of view, and to identify a motion condition of
an appropriate level when such an object or objects present.
[0040] It will be understood that these methods of detecting the
movement condition are especially applicable in the system
environment of a head-mounted digital display where the individual
frames are displayed as a series of bit planes. At the same time,
however, benefits of the invention may also be derived for other
types of display that are not head-mounted but in which frames are
displayed as serial bit planes, such as an LCD projected OTW
display.
[0041] In the preferred embodiment, the light engine 29 receives
the configured video from mapper 25, and also the movement
condition signal from image generator 23. From these signals, light
engine 29 controls the display of the video on display device 33,
which in the preferred embodiment is the display electronics and
visor 9 of the head-mounted display. The display device preferably
includes a microdisplay that may be LCD, LED, LCOS, or any of a
number of digital microdisplay devices, such as micromirror
displays (DMDs) made by Texas Instruments, that use bi-stable pixel
elements to form images as display of a series of bit planes for
each frame. The output of the light engine 29 is a direct
electronic control through the display driver of the on or off
condition of all the bi-stable pixel elements in the display device
33.
[0042] Particularly preferred for the display controller and
display device of the invention is a modified combination light
engine and microdisplay similar to that sold by CRL Opto Ltd., a
company having a place of business in Dunfermline, Scotland, in
which the light engine controls the order in which individual bit
planes are displayed on an LCOS microdisplay attached thereto, so
that, for example, a low-significance-bit red bit plane may be
displayed first, followed by the most significant red bit plane,
and then a red bit plane corresponding to another lower significant
bit, in whatever order is desired, with the totality of the bit
planes adding up to the frame image. An exemplary series of bit
planes that can be displayed by such a light engine is shown in
FIG. 6. In this particular display scheme, the most significant bit
of the digital data for each color of the pixels is displayed by
display of the same bit plane twice for that bit to increase the
total color of the displayed frame image, resulting in nine bit
planes displayed for each color in FIG. 6. The first and last bits
displayed are respectively the least significant bits for the
colors red and green. It will be understood, however, that the CRL
Opto product is modified to perform additional functions as
required by the present invention, as described below.
[0043] The present invention addresses the problem of perceived
degradation or color separation in a bit-plane display during a
period of high movement of the user's viewpoint or objects in the
OTW scene by reducing the frame display period, meaning the
duration between the beginning of the display or illumination of
the first bit plane of a given frame image and the end of display
or illumination of the last bit plane of the frame image.
[0044] As illustrated in FIG. 4, the video is displayed as a series
of frame images, one displayed for each video frame cycle, which in
the preferred embodiment is 60 Hz. Where a movement condition is
not detected, as, e.g., when the user is not moving his head very
rapidly, or when the OTW scene shown to the user is not moving
rapidly relative to the display screen or to the user's eyes, etc.,
the bit planes of the frame are displayed with the duration between
the first and last bit planes being a normal frame display period,
as indicated.
[0045] The image generator automatically and continuously or
cyclically checks in real time whether a high-movement condition is
detected, as described above, that might degrade the perception of
the video. When such a condition is detected (point A in FIG. 4),
display of the video is modified such that the duration between the
first and last bit planes of the frame is a shortened frame display
period, as indicated. This improves the separation effect perceived
by the user because, for movement at a high rate, the perceived
displacement distance between the first and last bit planes is
reduced with the reduction of the space of the time between the
display of the first and last bit planes.
[0046] When the high-movement condition is no longer detected
(point B in FIG. 4), the video is again displayed in its normal
mode, where the duration between the start of the first bit plane
and the end of the last bit plane is the normal frame display
period.
[0047] The frame display period is shortened during movement
conditions as illustrated in FIG. 5. When the image generator 23
detects a motion condition that may reduce the quality of the
perception of the display, it outputs a signal indicative of the
presence of the condition, and preferably also indicative of the
severity of the condition, e.g., increasing severity in motion
levels 1, 2 and 3 for head rotation rates above the lowest
threshold rate value, a middle threshold rate value, and a highest
threshold rate value. In normal mode for a generally static image,
the image generator outputs no signal, or a zero, and the display
is, in the example shown, a typical digital color display of 8 bit
planes per color, ranging from the highest peak (or
most-significant bit) to the lowest peak (or least significant bit)
for each color, with a total of 24 bit planes. Hardware limitations
require that each bit plane be displayed for a minimum amount of
time, and the full image, with all bit planes, is displayed in a
hardware-limited minimum display period indicated at point 35,
where the static image update for the frame image is complete.
[0048] When motion level 1 is detected, the image generator outputs
a 1, and the light engine 29 converts the video received along line
27 to be displayed in fewer bit planes. As seen in FIG. 5, in the
preferred embodiment, a motion level 1 results in a display of the
video using seven bit planes per color instead of eight. This
results in a shortening of the frame display period so that the
frame update is complete by time limit 37. It also results in a
reduction of the color depth and the range of possible colors of
the display from 16,581,375 to about 2 million possible colors, but
during a brief period of rapid movement this change in color depth
should not be detected by the user.
[0049] The reduced number of bit-planes may be produced by the
light engine 29 in a variety of ways. In one embodiment, each frame
of the displayed video is derived by dropping the last
least-significant bit of each set of eight bits defining the red,
green and blue intensities of each pixel, and as a consequence,
dropping out display of the least significant bit plane for each of
the three colors.
[0050] Alternatively, the video frames from mapper 25 are converted
by rescaling the number value of the color intensity for each pixel
from eight bits to a field of seven or fewer bits, as applicable to
the degree of shortening of display time applied, with rounding of
the resulting value up or down at the last bit as appropriate.
[0051] If the image generator 23 determines that the movement
condition is more severe, it outputs a number related to the
severity of the condition, for example, a 2, 3 or higher number as
the signal to the light engine 29, and the light engine displays
the video with fewer bit planes, resulting in an even more
abbreviated frame display period. As seen in FIG. 5, a motion level
2 condition results in the display being made up of six bit planes
per color per frame, with an even shorter display period updating
the frame within the time indicated at 39. Similarly, detection of
a motion level 3 condition will result in a display using only five
bit planes, update completed at a much shorter time 41. Even fewer
bit plane may be used, dependent on the acceptable quality of the
simulator.
[0052] The bit plane values for these higher motion levels may be
also derived from the video received by light engine 25 by dropping
the least significant bit planes to reduce the number of total bit
planes for the frame, but are most preferably derived by scaling
down the illumination value for each color for the pixel down to a
number of bits equal to the number of bit planes that are to be
displayed, rounding the value to the nearest scaled binary number.
For example, if the red illumination were defined by eight bits as
10101111.sub.2 (meaning decimal 175), the number would be scaled to
a five-bit value by dividing by 8, to yield 217/8, and rounding up
to 22, expressed in binary as 10110.sub.2.
[0053] As with the change to 7-bit color depth, there is a loss of
color depth in these reduced bit plane displays. Coupled with a
rearrangement of the bit planes as in FIG. 6 such that the first
and last bit planes are the lowest in intensity, the effects of
movement on the display are greatly reduced, and the quality of the
simulation is enhanced.
[0054] The image generator automatically tests for the presence of
the motion condition and its severity at least every frame display
cycle (e.g. at 60 H.sub.z). When the motion condition is no longer
detected as present, the condition signal is stopped or set to
zero, and the light engine 29 returns to normal display of the
video, e.g., eight bit planes per color. If the motion condition is
detected as having dropped in severity, then the condition output
is dropped to a lower value, and the display is changed to be made
with the number of bit planes corresponding to that motion
level.
[0055] The output signal from image generator 23 to light engine 29
may alternatively be a three-bit value representing the color depth
to display the video in. For example, normal static image video
would be displayed in 8-bit color depth responsive to a binary
111.sub.2, 7-bit color depth displayed responsive to a binary
110.sub.2, 6-bit to a 101.sub.2, 5-bit to a 100.sub.2, and so
on.
[0056] As an alternative to the above described system, one of
skill in the art will be able to accomplish similar benefits by
incorporating aspects and functions of the hardware in software
functions of the image generator. For example, the image generator
may internally detect the motion level of the video and calculate a
lower color-depth version of the video, and transmit that for
compressed display instead of providing that function in the light
engine.
[0057] It will be understood that the invention herein extends well
beyond the embodiments of the disclosure, and the terms used in
this specification should be understood to be language of
description, not limitation, as those of skill in the art with this
specification before them will be able to make changes and
modifications therein without departing from the scope of the
invention.
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